JPH09176094A - Continuous production of aromatic carbonate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method capable of efficiently producing an aromatic carbonate by reacting a dialkyl carbonate with an aromatic hydroxy compound. SOLUTION: When a dialkyl carbonate is reacted with an aromatic hydroxy compound in the presence of a catalyst in a reactor 1, the dialkyl carbonate and the aromatic hydroxy compound taken out from the reactor 1 are recovered and circulated to a reaction system, at least one purifying and circulating process of [I]a purifying and circulating process for separating and removing alcohols and alkyl aromatic ethers (anisoles) from the reaction mixture taken out from the top of the reactor 1 and circulating the prepared dialkyl carbonate to the reaction system and [111 a purifying and circulating process for separating and removing the alkyl aromatic ethers from the reaction mixture taken out from the bottom part of the reactor and circulating the dialkyl carbonate and/or the aromatic hydroxy compound to the reaction system is carried out.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a continuous method for producing an aromatic carbonate, and more particularly to an aromatic carbonate capable of continuously and efficiently producing an aromatic carbonate from a dialkyl carbonate and an aromatic hydroxy compound. It relates to a continuous production method of carbonate.

[0002]

TECHNICAL BACKGROUND OF THE INVENTION Diphenyl carbonate (DP
C) is a compound industrially useful as a raw material for producing polycarbonate, and it is industrially valuable to produce diphenyl carbonate with high productivity.

It is conventionally known that such a diphenyl carbonate can be obtained by reacting a dialkyl carbonate with an aromatic hydroxy compound. For example, when dimethyl carbonate is reacted with phenol, methylphenyl carbonate, diphenyl carbonate, or a mixture thereof is obtained as described below.

[0004]

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However, the above-mentioned reactions are all equilibrium reactions, and there is a problem that the reaction is biased to the original system and the reaction rate is slow. In order to solve such problems, various catalysts that can increase the reaction rate have been proposed.

Attempts have also been made to separate and distill off alcohols such as methyl alcohol produced as a by-product from the reaction from the starting materials, products or solvents to allow the reaction to proceed to the production system side. It is also known to use a reactor.

Further, in Japanese Patent Laid-Open No. 3-291257, a continuous multi-stage distillation column is used, and alcohols and the like by-produced by the reaction are continuously withdrawn by distillation to allow the reaction product to proceed to the production system side. Has been proposed for continuously producing aromatic carbonate by continuously extracting the aromatic carbonate.

By the way, in the above continuous production method of aromatic carbonate, in addition to the reaction product and by-product alcohol, unreacted raw materials (including dialkyl carbonate produced as a by-product of the reaction), catalyst, solvent and the like are also used. Since they are recovered from the reaction apparatus, it is possible to efficiently carry out the continuous aromatic carbonate production method by circulating these unreacted raw materials again in the reaction system.

The present inventor has studied the continuous production method of such an aromatic carbonate. When the continuous operation is carried out while circulating the recovered unreacted raw material in the reaction system, the production efficiency of the aromatic carbonate is increased. I found that it would decrease. The present inventor has further investigated the cause of this, and in the reaction of the dialkyl carbonate and the aromatic hydroxy compound, an alkyl aromatic ether such as anisole is by-produced although the selectivity is low. It has been found that there is a cause that the reaction raw material is circulated in the reaction system and is continuously operated to be accumulated in the reactor to reduce the effective volume of the reactor. And after separating and removing the alkyl aromatic ether from the unreacted raw material extracted from the reactor based on such knowledge, the continuous production method of the aromatic carbonate efficiently by circulating the unreacted raw material in the reaction system. The inventors have found that they can be performed and have completed the present invention.

[0010]

DISCLOSURE OF THE INVENTION The present invention has been made based on the above research, and provides a method for producing an aromatic carbonate efficiently and continuously by reacting a dialkyl carbonate with an aromatic hydroxy compound. It is intended to be provided.

[0011]

SUMMARY OF THE INVENTION In the continuous production method of aromatic carbonate according to the present invention, a dialkyl carbonate and an aromatic hydroxy compound are reacted in the presence of a catalyst in a reaction device, and the reaction product is produced from the reaction device. Aromatic carbonate, by-produced alcohols, dialkyl carbonate and aromatic hydroxy compound are continuously extracted, and dialkyl carbonate and aromatic hydroxy compound are recovered and circulated to the reaction system to continuously produce aromatic carbonate. At this time, [I] alcohols and alkyl aromatic ethers are separated and removed from a reaction mixture containing by-produced alcohols extracted from the upper part of the reaction device, dialkyl carbonate and alkyl aromatic ethers by-produced in the reaction device. Anti dialkyl carbonate Purification and circulation step of circulating in the system, and [II] distilling the reaction mixture containing aromatic carbonate, dialkyl carbonate, aromatic hydroxy compound withdrawn from the lower part of the reactor and alkyl aromatic ether by-produced in the reactor. While separating the aromatic carbonate from the bottom of the distillation column, the alkyl aromatic ether is separated and removed from the reaction mixture obtained from the top of the distillation column,
A purification circulation step of circulating the obtained dialkyl carbonate and / or aromatic hydroxy compound in the reaction system,
Among them, at least one refining and circulation step is performed.

In the present invention, aromatic carbonates include alkyl aryl carbonates, diaryl carbonates,
Or a mixture of these. The dialkyl carbonate is preferably dimethyl carbonate or diethyl carbonate.

The aromatic hydroxy compound is phenol,
It is preferably m- and / or p-cresol.
A representative example of an alkyl aromatic ether is anisole.

In the present invention, in the above continuous production method of aromatic carbonate, two reactors are used,
In the first reactor, a dialkyl carbonate is reacted with an aromatic hydroxy compound in the presence of a catalyst to produce an alkylaryl carbonate as an aromatic carbonate, and then in a second reactor, the alkylaryl carbonate is obtained in the first reactor. It is preferable to react the obtained alkylaryl carbonate or to react the alkylaryl carbonate with an aromatic hydroxy compound to generate a diaryl carbonate as an aromatic carbonate.

[0015]

DETAILED DESCRIPTION OF THE INVENTION The continuous method for producing an aromatic carbonate according to the present invention comprises reacting a dialkyl carbonate with an aromatic hydroxy compound in the presence of a catalyst in a reaction device, and producing the reaction product from the reaction device. Aromatic carbonate, by-produced alcohols, dialkyl carbonate and aromatic hydroxy compound are continuously extracted, and dialkyl carbonate and aromatic hydroxy compound are recovered and circulated to the reaction system to continuously produce aromatic carbonate. During production, [I] alcohols and alkyl aromatic ethers are separated and removed from a reaction mixture containing by-produced alcohols extracted from the upper part of the reaction device, dialkyl carbonate and alkyl aromatic ethers by-produced in the reaction device. , The obtained dialkyl carbonate And a reaction mixture containing an aromatic carbonate, a dialkyl carbonate, an aromatic hydroxy compound extracted from the lower part of the reactor and an alkyl aromatic ether by-produced in the reactor. The aromatic carbonate is separated by distillation from the bottom of the distillation column, and the alkyl aromatic ether is separated and removed from the reaction mixture obtained from the top of the distillation column, and the obtained dialkyl carbonate and / or aromatic hydroxy compound is added to the reaction system. At least one of the refining and recycling steps of circulating the refining and recycling step is performed.

First, the dialkyl carbonate, aromatic hydroxy compound, and catalyst used in the production of the aromatic carbonate in the present invention will be described. In the present invention, a dialkyl carbonate represented by the following general formula (i) is used.

[0017]

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[0018] (R ^1, R ² is an alkyl group, an alkenyl group, an alicyclic group, aralkyl group, or different an each identical with R ¹ and R ^2, R ¹ and R
² and may form a ring. ) As R ¹ and R ² , specifically, a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group,
Alkyl groups such as heptyl group, octyl group, nonyl group and decyl group, alkenyl groups such as allyl group and butenyl group,
Cyclopropyl group, cyclobutyl group, cyclopentyl group, cyclohexyl group, alicyclic group such as cycloheptyl group, alicyclic group-containing alkyl group such as cyclohexylmethyl group, benzyl group, phenethyl group, phenylpropyl group, phenylbutyl group, Examples thereof include aralkyl groups such as methylbenzyl group.

Further, these groups may be substituted with a lower alkyl group, a lower alkoxy group, a cyano group or a halogen atom, and may have an unsaturated bond. Examples of the dialkyl carbonate represented by the formula (i) include:
For example, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, diallyl carbonate,
Dibutenyl carbonate, dibutyl carbonate, dipentyl carbonate, dihexyl carbonate, diheptyl carbonate, dioctyl carbonate, dinonyl carbonate, didecyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, methyl butyl carbonate, ethyl propyl carbonate, ethyl butyl carbonate, ethylene carbonate , Propylene carbonate, di (methoxymethyl) carbonate,
Di (methoxyethyl) carbonate, di (chloroethyl) carbonate, di (cyanoethyl) carbonate,
Dicyclopentyl carbonate, dicyclohexyl carbonate, dicycloheptyl carbonate, dibenzyl carbonate, diphenethyl carbonate, di (phenylpropyl) carbonate, di (phenylbutyl) carbonate, di (chlorobenzyl) carbonate, di (methoxybenzyl) carbonate, etc. To be

Two or more of these may be used in combination. Among these, dialkyl carbonates in which each of R ¹ and R ² is an alkyl group having 4 or less carbon atoms are preferable, dimethyl carbonate and diethyl carbonate are more preferable, and dimethyl carbonate is particularly preferable.

The aromatic hydroxy compound used in producing the aromatic carbonate is represented by the following general formula (ii). Ar ¹ OH (ii) Ar ¹ is a monovalent aromatic group, and the aromatic group may have a substituent.

Examples of such aromatic monohydroxy compounds include phenol, cresol, xylenol, trimethylphenol, tetramethylphenol,
Ethylphenol, propylphenol, butylphenol, diethylphenol, methylethylphenol,
Alkylphenols such as methylpropylphenol, dipropylphenol, methylbutylphenol, pentylphenol, hexylphenol, cyclohexylphenol, alkoxyphenols such as methoxyphenol and ethoxyphenol, naphthols, substituted naphthols,

[0023]

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(Here, R ⁴ , R ⁵ , R ⁶ , and R ⁷ are a hydrogen atom, a lower alkyl group, a cycloalkyl group, an aryl group, and an aralkyl group, respectively, and these are a halogen atom,
It may be substituted with an alkoxy group. K is 3 to 1
It is an integer of 1, and the hydrogen atom may be substituted with a lower alkyl group, an aryl group, a halogen atom or the like. ) Further, the aromatic ring has a lower alkyl group, a lower alkoxy group, an ester group, a hydroxyl group, a nitro group, a halogen atom,
It may be substituted with a substituent such as a cyano group. ] Heteroaromatic hydroxy compounds such as hydroxypyridine, hydroxycoumarin, hydroxyquinoline and the like can be mentioned.

Further, an aromatic dihydroxy compound can be used, and for example, hydroquinone, resorcin, catechol, dihydroxynaphthalene, dihydroxyanthracene, and an alkyl-substituted product thereof, and aromatic dihydroxy compounds represented by the following formula can be used.

[0026]

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(A is the same as A above, and the aromatic ring is
It may be substituted with a substituent such as a lower alkyl group, a lower alkoxy group, an ester group, a hydroxyl group, a nitro group, a halogen atom and a cyano group. ) In the present invention, among these, Ar ¹ in the above formula (ii) is
Is preferably an aromatic monohydroxy compound consisting of an aromatic group having 6 to 10 carbon atoms, phenol, m-and / or
P-cresol is preferred, and phenol is particularly preferred.
Further, two or more aromatic hydroxy compounds can be used in combination.

In the present invention, the aromatic hydroxy compound as described above may be supplied to the reaction system in a molar ratio of dialkyl carbonate / aromatic hydroxy compound of 10 to 1, preferably 5 to 1.5. desirable.

From the above-mentioned dialkyl carbonate and aromatic hydroxy compound, alkylaryl carbonate and diaryl carbonate are produced by the following reaction. The case where a dialkyl carbonate in which R ¹ and R ^{2 in} formula (i) are the same is used as the dialkyl carbonate is shown below.

[0030]

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Specific examples of the alkyl aryl carbonate obtained by the above reaction formula (1) include methylphenyl carbonate, ethylphenyl carbonate,
Propyl phenyl carbonate, allyl phenyl carbonate, butyl phenyl carbonate, pentyl phenyl carbonate, hexyl phenyl carbonate, heptyl phenyl carbonate, octyl rill carbonate, nonyl (ethyl phenyl) carbonate, decyl (butyl phenyl) carbonate, methyl tolyl carbonate, ethyl tolyl carbonate, Propyl tolyl carbonate, butyl tolyl carbonate, allyl tolyl carbonate, ethyl xylyl carbonate, methyl (trimethylphenyl) carbonate, methyl (chlorophenyl) carbonate, methyl (nitrophenyl) carbonate, methyl (methoxyphenyl) carbonate, methyl cumyl carbonate, methyl (Naphthyl) carbonate, methyl (pi Jill) carbonate, ethyl cumyl carbonate, methyl (benzoylphenyl) carbonate, ethyl xylyl carbonate, benzyl xylyl carbonate, methyl (hydroxymethyl phenyl) carbonate, ethyl (hydroxy phenyl) carbonate,
Methoxycarbonyloxybiphenyl, methyl (hydroxybiphenyl) carbonate, methyl 2- (hydroxyphenyl) propylphenyl carbonate, ethyl 2-
(Hydroxyphenyl) propyl phenyl carbonate etc. are mentioned.

Specific examples of the diaryl carbonate obtained by the reaction formula (2) or (3) include diphenyl carbonate, ditolyl carbonate, phenyltolyl carbonate, di (ethylphenyl) carbonate,
Phenyl (ethylphenyl) carbonate, dinaphthyl carbonate, di (hydroxyphenyl) carbonate, di [2- (hydroxyphenylpropyl) phenyl]
Carbonate and the like.

The above examples also include the case where an aromatic dihydroxy compound is used as the aromatic hydroxy compound. The aromatic carbonate produced in the present invention is the above-mentioned alkylaryl carbonate, diaryl carbonate, or a mixture thereof.

In the present invention, in the above reaction, alcohols having a boiling point lower than that of the aromatic carbonate as a reaction product are by-produced, the aromatic carbonate is extracted from the lower part of the reactor and the by-product is produced from the upper part of the reactor. It is preferable to use a raw material from which alcohols can be extracted. Specifically, in the above reaction, it is preferable that the alkylaryl carbonate is methylphenyl carbonate and the diaryl carbonate is diphenyl carbonate.

As the aromatic carbonate, it is preferable to finally produce a diaryl carbonate. The reaction between the dialkyl carbonate and the aromatic hydroxy compound as described above is usually carried out in the liquid state in the presence of a catalyst.

In the present invention, as the catalyst, any known catalyst can be widely used without particular limitation as long as it is a catalyst capable of producing aromatic carbonates. The catalyst used in the present invention may be one that is soluble in the reaction solution under reaction conditions (homogeneous system) or one that is insoluble in the reaction solution (heterogeneous system).

Examples of the catalyst include Lewis acids, tin compounds, lead compounds, copper group metal compounds, alkali metal complexes, zinc complexes, iron group metal compounds, zirconium complexes and solid catalysts. More specifically, Lewis acids include AlX ₃ , TiX ₃ , TiX ₄ , VOX ₃ ,
Examples include Lewis acids such as VX ₅ , ZnX ₂ , FeX ₃ , and SnX ₄ (where X is a halogen atom, an acetoxy group, an alkoxy group, and an aryloxy group) and transition metal compounds that generate a Lewis acid. More specifically, titanium tetrachloride, tetraphenoxy titanium (Ti (OPh) ₄ ),
Tetracrezoxy titanium, tetramethoxy titanium, tetraethoxy titanium, tetraisopropoxy titanium, tetradodecyloxy titanium, tetraisooctyloxy tin,
Examples include triisopropoxy aluminum.

Examples of the tin compound include organic tin compounds such as trimethyltin acetate, triethyltin acetate, tributyltin acetate, triphenyltin acetate, dibutyltin diacetate, dibutyltin dilaurate, dioctyltin dilaurate, dibutyltin adipate, dibutyldimethoxytin. , Dibutyldiphenoxytin, [(Bu ₂ Sn (OP
h)] ₂ O, dimethyltin glycolate, dibutyldiethoxytin, triethyltin hydroxide, hexaethylstannoxane, hexabutylstannoxane, dibutyltin oxide (Bu ₂ SnO), dioctyltin oxide, butyltin triisooctylate , Octyltin triisooctylate, butylstannonic acid, octylstannonic acid, polymeric tin compounds such as poly [oxy (dibutylstannylene)], polymeric hydroxy such as poly (ethylhydroxystannoxane) Stanoxane etc. are mentioned. Further, tin oxide may be used as the tin compound.

As the lead compound, PbO, PbO_Two, P
b_ThreeO_FourLead oxides such as PbS, Pb_TwoLead sulfide such as S
Type, Pb (OH)_Two, Pb_TwoO_Two(OH)_TwoHydroxylation
Leads, Na_TwoPbO_Two, K_TwoPbO_Two, NaHPbO_Two,
KHPbO_TwoNamarites such as Na_TwoPbO_Three,
Na_TwoH_TwoPbO_Four, K_TwoPbO_Three, K_Two[Pb (O
H)₆], K_FourPbO_Four, Ca_TwoPbO_Four, CaPbO_Three
Lead salts such as PbCO _Three2PbCO_Three・ Pb (O
H)_TwoLead carbonates and basic salts thereof, such as Pb (O
COCH_Three)_Two, Pb (OCOCH_Three)_Four, Pb (OCO
CH_Three)_Two・ PbO ・ 3H_TwoLead salts of organic acids such as O and
Lead carbonate and its basic salts, R_FourPb, R_ThreePbCl
 , R_ThreePbBr, R_ThreePb or R₆Pb_Two, R_ThreePbO
H, R_ThreePbO (where R is C_FourH₉Alkyl groups such as
Or organic lead compounds such as aryl groups such as phenyl)
, Pb (OCH_Three)_Two, (CH_ThreeO) Pb (OPh),
Pb (OPh)_TwoAlkoxy Leads such as Aryl Oki
Sileads, Pb-Na, Pb-Ca, Pb-Ba, Pb-
Lead alloys such as Sn and Pb-Sb, phoenite, sena
Lead minerals such as ene ore and hydrates of these lead compounds
And the like.

As the copper group metal compound, CuCl, Cu
Cl ₂ , CuBr, CuBr ₂ , CuI, CuI ₂ , Cu
(OAc) ₂ , Cu (acac) ₂ , copper olefinate,
Bu ₂ Cu, (CH ₃ O) ₂ Cu, AgNO ₃ , AgBr
Picric _{silver, AgC 6 H 6 ClO 4 Ag} ( bullvalene) ₃ NO _3, [AuC≡C-C (CH _{3) 3] n} [Cu
Examples include salts and complexes of copper group metals such as (C ₇ H ₈ ) Cl] ₄ (where acac is an acetylacetone chelate ligand).

As the alkali metal complex, Li (aca
c), LiN (C ₄ H ₉ ) _{2 and the} like. Examples of the zinc complex include Zn (acac) ₂ .

As the cadmium complex, Cd (aca
c) _{2 and the} like. As the iron group metal compound, F
e (C ₁₀ H ₈ ) (CO) ₅ , Fe (CO) ₅ , CoC ₅ F
₆ ) (CO) ₇ , Ni—C ₅ H ₅ NO, ferrocene and the like.

As the zirconium complex, Zr (aca
c) ₄ , and zirconocene. As the solid catalyst, silica, alumina, titania, silica-titania,
Examples thereof include zinc oxide, zirconium oxide, gallium oxide, zeolite and rare earth oxides.

Of these, homogeneous catalysts are preferred.
Especially tetraphenoxy titanium, tetramethoxy titanium
Lewis acids such as benzene, Bu_TwoSnO, [(Bu_TwoSn (OP
h)] _TwoOrganotin compounds such as O, Pb (OPh)_TwoWhat
Any alkoxy lead or the like is preferably used.

These catalysts can be used as a mixture with a compound inert to the reaction or a carrier, or can be used by being carried on a carrier. Further, the catalyst may be one that can react with the reaction raw materials and reaction products present in the reaction system, and may be previously heat-treated with the reaction raw materials and reaction products.

In the present invention, when a homogeneous catalyst is used as the catalyst, for example, it can be present in the reaction system by continuously supplying the catalyst into the reaction apparatus, and when a heterogeneous catalyst is used. Can be present in the reaction system by being placed in the reactor.

When the homogeneous catalyst is continuously fed into the reactor, the reaction starting materials such as dialkyl carbonate and / or
Alternatively, the aromatic hydroxy compound may be mixed and supplied, or may be separately supplied.

The catalyst as described above varies depending on its type, reaction conditions, etc., but when a homogeneous catalyst is continuously fed into the reaction apparatus, it is usually mixed with the aromatic hydroxy compound which is a reaction raw material. , 0.001 to 10 mol%, preferably 0.01 to 5 mol%. Heterogeneous catalysts are usually used in an amount of 0.0
It is arranged in an amount of 1 to 75% by volume.

The reaction between the dialkyl carbonate and the aromatic hydroxy compound, which is carried out in the presence of the catalyst as described above, is carried out in the reactor. As the reaction device, a reactive distillation column, a continuous reaction device with a distillation column, or the like can be used, but it is preferable to use a reactive distillation column.

As the reactive distillation column, it is preferable to use an apparatus having a large gas-liquid interface area so that the reaction can be easily transferred to the production system side. Specifically, a multi-stage distillation reaction column having two or more distillation stages can be used, and a known multi-stage distillation such as a plate column type, a packed column type, or a combination of a plate column type and a packed column type is used. A reaction tower can be used. In such a multistage distillation reaction column, it is preferable that the catalyst is present in all stages. When a solid catalyst is used in a packed column system, the solid catalyst may be a part or the whole of the packing.

The above reaction can be carried out in the presence of a solvent, if necessary. As this solvent, a reaction inert solvent can be used, and for example, ethers, aliphatic hydrocarbons, halogenated aromatic hydrocarbons and the like can be used.

It is also possible to carry out the reaction in the presence of a reaction-inert gas such as nitrogen, helium or argon. The reaction conditions will differ depending on the type of reactor used, structure, reaction raw materials, etc., but are usually 50 to 350 ° C., preferably 100 to 280 ° C., and particularly preferably 150 to 280 ° C.
At the reaction temperature (internal temperature). Decompression, normal pressure,
It may be under pressure, but usually 2600 Pa to
It is carried out under a pressure of 5.4 MPa. The average residence time in the reactor is usually 0.001 to 50 hours, preferably 0.01 to 10 hours, more preferably about 0.05 to 5 hours.

In the present invention, the reaction (1) to (3) can be carried out by using one reactor to produce the aromatic carbonate, and the aromatic carbonate can be prepared by using two or more reactors. Can also be manufactured. In the present invention, using two reactors, the reaction (1) is performed in the first reactor to produce mainly alkylaryl carbonate, and the reactions (2) and (3) are performed in the second reactor. It is preferred to do so to produce the diaryl carbonate.

The aromatic carbonate produced in the reactor as described above is continuously withdrawn from the reactor, and this aromatic carbonate is usually withdrawn in liquid form from the lower part of the reactor. The aromatic carbonate withdrawn from the reactor can also be introduced into a purification column for purification.

On the other hand, the by-product alcohols are usually withdrawn from the upper part of the reactor. The aromatic hydroxy compound and the dialkyl carbonate, which are unreacted raw materials, are continuously withdrawn from the reactor, separated and recovered, and circulated in the reaction system. The dialkyl carbonate includes not only unreacted raw materials but also those by-produced in the reaction. Hereinafter, the dialkyl carbonate recovered from the reactor may be referred to as an unreacted raw material.

In the present invention, when the unreacted raw material is collected and circulated in the reaction system as described above, the unreacted raw material and the inside of the reactor (especially the first reactor when two reactors are used) are used. After separating the alkyl aromatic ether by-produced in step 1, the unreacted raw materials are circulated in the reaction system.

The alkyl aromatic ether is a dialky
L-carbonate and aromatic hydroxy compound Ar¹OH and
Is produced as a by-product at a low selectivity when Ar is reacted,
¹OR ¹Or Ar¹OR^Two, But for example
When reacting chill carbonate and phenol
Produces the following anisole.

[0058]

[Chemical 6]

The reaction product (aromatic carbonate), by-produced alcohols, unreacted raw materials (dialkyl carbonate and aromatic hydroxy compound) and by-produced alkyl aromatic ether as described above are added to the reaction mixture from the upper and lower portions of the reaction apparatus. In the present invention, the unreacted raw material obtained is circulated in the reaction system after separating each component from the reaction mixture in the purification and circulation step in the present invention. Specifically, [I] alcohols and alkyl aromatic ethers are separated and removed from a reaction mixture containing by-produced alcohols extracted from the upper part of the reaction device, dialkyl carbonate, and alkyl aromatic ethers by-produced in the reaction device. Then, a refining and circulation step in which the obtained dialkyl carbonate is circulated in the reaction system, and [II] aromatic carbonate, dialkyl carbonate, aromatic hydroxy compound extracted from the lower part of the reaction device, and alkyl aroma produced as a by-product in the reaction device. The reaction mixture containing the aromatic ether is distilled to separate the aromatic carbonate from the bottom of the distillation column, and the alkyl aromatic ether is separated and removed from the reaction mixture obtained from the top of the distillation column to obtain the dialkyl carbonate and / or the aroma. Purification by circulating group hydroxy compounds in the reaction system At least one refining / circulating step of the refining / recycling step [I] or the refining / recycling step [II] is performed independently of the refining / recycling step [I] and the refining / recycling step [II]. It is preferable to do both.

In each purification and circulation step, the aromatic carbonate, alcohols, dialkyl carbonate, aromatic hydroxy compound and alkylaromatic ether can be usually separated by distillation. Further, the reaction mixture extracted from the reaction apparatus may be separated into each component by one distillation apparatus, or each component may be sequentially separated by using two or more distillation apparatuses. For example, when separating and removing alcohols and alkyl aromatic ethers from the reaction mixture extracted from the upper part of the reactor, the alcohols are once separated from the reaction mixture extracted from the upper part of the reactor and then the alcohol is removed. The alkyl aromatic ether can be removed from the reaction mixture from which the class has been removed, and the resulting dialkyl carbonate can be recycled to the reaction system.

Hereinafter, a specific example of the continuous method for producing an aromatic carbonate according to the present invention will be described with reference to FIG. 1 in the case of producing an aromatic carbonate from dimethyl carbonate and phenol by using two reactors. While explaining concretely.

In FIG. 1, the lower line 1 is connected to the reactor 1.
Dimethyl carbonate is continuously introduced from 1 and phenol and a homogeneous catalyst are continuously introduced from line 12, and dimethyl carbonate and phenol are reacted in the reactor 1. The raw materials may be introduced from the same line.

The reaction mixture extracted from the upper part 13 (preferably the top of the column) of the reactor 1 (hereinafter referred to as reaction mixture A) contains unreacted and by-produced dimethyl carbonate, by-produced methyl alcohol, and anisole. There is.

The reaction mixture A is once introduced into the distillation column 2 and the by-product methyl alcohol is removed from the line 21. In this distillation, part of dimethyl carbonate is also distilled off by azeotropic distillation (7: 3) of methyl alcohol and dimethyl carbonate.

Dimethyl carbonate in the distillation residue,
Since anisole (alkyl aromatic ether) and the like are concentrated, by distilling the distillation residue again, anisole can be removed and high-purity dimethyl carbonate can be obtained (first purification cycle). Step [I-1]).

Specifically, the distillation residue is supplied from the lower part of the distillation column 2 to the distillation column 3 via the line 22 to separate dimethyl carbonate and anisole. Anisole can be removed from the line 32, and high-purity dimethyl carbonate can be circulated to the reactor 1 from the line 31.

In the refining and circulation step [I-1], for example, dimethyl carbonate (boiling point 90 to 91 ° C.) and anisole (155.5 ° C.) can be easily separated because of a large boiling point difference. The dimethyl carbonate purified in the refining and recycling step [I-1] can be circulated in the reaction system for reuse.

On the other hand, the reaction mixture (reaction mixture B) withdrawn from the lower part of the reactor, preferably the bottom part of the reactor, via line 14 is usually methylphenyl carbonate, diphenyl carbonate, dimethyl carbonate, phenol, by-produced anisole, Contains catalysts.

This reaction solution is once distilled in the distillation column 4, and a distillate containing dimethyl carbonate, phenol and anisole is usually distilled off from the upper part of the distillation column 4 through a line 41. Is led to the purification circulation step [II]. When distilling in the distillation column 4, a small amount of anisole is also contained in the bottom distillate.

In the purification circulation step [II], the distillation column 4
Dimethyl carbonate, phenol and anisole are separated by distillation from the upper distillate obtained from. More specifically, in the distillation column 5, first, dimethyl carbonate and the dimethyl carbonate are respectively distilled off from the upper portion of the distillation column 5 to be separated, and can be recycled to the reaction device 1 via the line 51. On the other hand, the distillate distilled off from the lower part of the distillation column 5 is then supplied to the distillation column 6, where anisole and phenol are distilled and separated, and the anisole is separated and removed from the upper part of the distillation column 6. The phenol can be distilled off from the lower part of the distillation column 6, and the obtained phenol can be circulated to the reaction apparatus 1 via the line 62.

On the other hand, the reaction liquid distilled off from the bottom of the distillation column 4 through the line 42 contains methylphenyl carbonate, diphenyl carbonate, dimethyl carbonate, phenol, anisole and the like.
Is introduced into the reactor 7.

In the second reactor 7, methylphenyl carbonate is mainly reacted with phenol supplied with phenol from the line 73 to produce diphenyl carbonate. In the second reaction device 7, a reaction for producing diphenyl carbonate by a reaction between methylphenyl carbonates is also performed.

From the upper part 71 of the second reactor 7,
Anisole is also distilled off together with dimethyl carbonate and phenol, but this distillate is introduced to the purification and circulation step [I-2] to remove anisole in the same manner as in the purification and circulation step [II]. Phenol can be recovered. Specifically, the distillate distilled off from the reactor top 71 can be distilled in the distillation column 8, and dimethyl carbonate can be circulated from the distillation column upper part 81 to the line 11 of the reactor 1. Also, the lower part 8 of the distillation column
2, phenol and anisole are introduced into the distillation column 9 and separated by distillation, and the separated phenol is separated from the lower part of the distillation column 92.
To the line 12 of the reactor 1. Anisole is removed from the distillation column upper part 91.

On the other hand, the aromatic carbonate obtained in the reactor 7 can then be refined in a purifying column (not shown). In the above-mentioned purification circulation steps [II] and [I-2], as shown in FIG. 2, for example, the multistage distillation column 10 separates dimethyl carbonate, phenol, and a mixture of anisole and phenol to separate and remove anisole. You may.

[0075]

INDUSTRIAL APPLICABILITY According to the present invention, in the continuous production method of aromatic carbonate, a specific by-product (alkyl aromatic ether) is removed from the recovered unreacted raw material and circulated in the reaction system. Carbonates can be efficiently and continuously produced.

[0076]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to the examples.

[0077]

Example 1 An aromatic carbonate was produced by a process using two reactors as shown in FIG.

As a methylphenyl carbonate (PMC) generator (reactor), a 500 ml autoclave equipped with a tray tray having a tower height of 3 m and a tower diameter of 2 inches, equipped with a sieve tray having 40 trays was used. .

The reaction solution was continuously withdrawn through an extraction tube provided at the bottom of the autoclave column. The low boiling point component containing by-product alcohol was withdrawn from the top of the distillation column, liquefied with a cooler, a part was withdrawn, and the rest was refluxed to the distillation column (reflux ratio = 1). The autoclave and the distillation column were heated by an electric furnace, and the temperature at the bottom of the distillation column was controlled to be 206 ° C. Further, the line for supplying the raw material was also heated by a heater.

Initially, phenol (PhOH) and Ti (OPh) ₄ as a catalyst were continuously fed at a rate of 293 g / hour (including 280 g of phenol and 13 g of catalyst) at the 20th stage of the distillation column. The upper 20 stages were used as a distillation column.

Dimethyl carbonate (DMC) is 122
An amount of 0 g / h was continuously fed to the autoclave.
Phenol did not evaporate at the top of the tower, and DMC / PhOH at the bottom of the tower
As a result of operating so that the molar ratio was about 1, 973 g / hour from the top of the distillation column and 540 g from the bottom of the distillation column.
The product was obtained at a rate of / hour. The amount of methylphenyl carbonate produced in the bottom liquid was 95 g / hour,
The amount of anisole produced was about 0.3 g / hour.

At the beginning of the reaction, DMC and methanol (MeOH) were the main components at the top of the column, and anisole was about 0.1.
It was included at 1 g / hour. Further, the distillate from the top of the distillation column is distilled at atmospheric pressure to separate an azeotropic mixture of MeOH and DMC, and then further distilled to obtain a pure DMC component, which is then used in a methylphenyl carbonate generator. Recycled.

On the other hand, the bottom liquid of the methylphenyl carbonate generator was concentrated to about 700 g / hour by simple distillation. Since the low boiling point component (about 270 g / hour) was mainly composed of DMC, it was returned to the methylphenyl carbonate generator as recovered DMC, and the concentrated component was supplied to the diphenyl carbonate generator.

In the production process of diphenyl carbonate (DPC), as a reaction device, the number of theoretical plates having an inner diameter of 2 inches is 2
Using a 500 m1 autoclave having a 5-stage packed distillation column, the concentrated liquid was supplied from the middle stage of the distillation column, and the column top pressure was 1
The reaction was carried out under the conditions of 10 torr, bottom temperature of 200 ° C., residence time of 1.5 hours and reflux ratio = 1. The amount of distillate from the top of the tower is about 50
It was 0 g / hour, and the distillation amount from the column bottom was about 200 g / hour.

Since the main component of the distillate from the top of the column was phenol, it was returned to the methylphenyl carbonate production step as recycled phenol. As a result, the rate of anisole accumulation slowed down, and the concentration of anisole at the bottom of the methylphenyl carbonate generator tower settled at 0.5% or less (Table 1).

[0086]

[Table 1]

[0087]

Comparative Example 1 In Example 1, the distillate from the top of the PMC reaction column was distilled at atmospheric pressure to separate the azeotrope of MeOH and DMC, and the remainder was used as it was to obtain methyl phenyl carbonate as DMC. Returned to the generator. When continuous operation was carried out under the above conditions, it was found that the concentration of methylphenyl carbonate decreased with time due to the accumulation of anisole (Table 2).

[0088]

[Table 2]

[Brief description of the drawings]

FIG. 1 is a process flow chart showing an embodiment of the method for producing an aromatic carbonate according to the present invention.

FIG. 2 shows another example of the distillation process in the purification circulation step [II] or [I-2].

Claims (6)

[Claims] 1. A reaction apparatus in which a dialkyl carbonate and an aromatic hydroxy compound are reacted in the presence of a catalyst, and an aromatic carbonate produced by the reaction, an alcohol by-produced, a dialkyl carbonate and When the aromatic hydroxy compound is continuously withdrawn and the dialkyl carbonate and the aromatic hydroxy compound are recovered and circulated in the reaction system to continuously produce the aromatic carbonate, [I] the auxiliary compound withdrawn from the upper part of the reaction device Purification and circulation step in which alcohols and alkyl aromatic ethers are separated and removed from a reaction mixture containing raw alcohols, dialkyl carbonates and alkyl aromatic ethers produced as a by-product in a reactor, and the resulting dialkyl carbonates are circulated in the reaction system, And [II]
Aromatic carbonate extracted from the bottom of the reactor, a dialkyl carbonate, an aromatic hydroxy compound and a reaction mixture containing an alkylaromatic ether by-produced in the reactor are distilled to separate the aromatic carbonate from the bottom of the distillation column. At least one purification circulation step of separating and removing the alkyl aromatic ether from the reaction mixture obtained from the upper part of the distillation column, and circulating the obtained dialkyl carbonate and / or aromatic hydroxy compound in the reaction system. A continuous process for producing an aromatic carbonate, characterized in that 2. The continuous process for producing an aromatic carbonate according to claim 1, wherein the aromatic carbonate is an alkylaryl carbonate, a diaryl carbonate, or a mixture thereof. 3. The continuous method for producing an aromatic carbonate according to claim 1, wherein the dialkyl carbonate is dimethyl carbonate or diethyl carbonate. 4. The aromatic hydroxy compound is phenol,
The continuous method for producing an aromatic carbonate according to claim 1, which is m- and / or p-cresol. 5. The alkyl aromatic ether is anisole,
The continuous process for producing an aromatic carbonate according to claim 1, which is phenetole, methyl tolyl ether or ethyl tolyl ether. 6. The method according to claim 1, wherein two reactors are used, and in the first reactor, a dialkyl carbonate and an aromatic hydroxy compound are reacted in the presence of a catalyst to produce an alkylaryl carbonate as an aromatic carbonate. Then, secondly, in the reactor, reacting the alkylaryl carbonate obtained in the first reactor or reacting the alkylaryl carbonate with an aromatic hydroxy compound to produce a diaryl carbonate as an aromatic carbonate. The continuous method for producing an aromatic carbonate according to claim 1, characterized in that.